Heretofore, in cultivation of crop plants in cropland, it has been desired to control weeds which inhibit the growth or the harvest of crop plants. Further, in non-cropland also, it is beneficial for utilization of the non-cropland to effectively control weeds. Thus, control of weeds is necessary in each of cropland and non-cropland, and various herbicides have been used. However, in recent years, there is a movement to reduce the dosage of a herbicidally active ingredient as far as possible, so as to reduce the environment load at a site where the herbicide is applied or the periphery thereof. For example, it is known to blend a nonionic surfactant to a spray solution thereby to improve the herbicidal effect and to reduce the dosage of the herbicide. As a general purpose product, an alkyl aryl polyglycol ether type surfactant (tradename: CITOWETT, manufactured by BASF France) or a silicon type surfactant (tradename: SILWETT L-77, polyalkylene oxide modified heptamethyl-trisiloxane, manufactured by Helena Chemical Company) may, for example, be mentioned.
The compound represented by the following formula (I) or its salt is disclosed in Patent Documents 1 to 4, but it is not known that its herbicidal effect is remarkably improved by a polyoxyalkylene alkyl ether phosphate or its salt.
Patent Document 5 discloses a herbicidal mixture comprising a 3-hetero ring-substituted benzoyl derivative or its salt, and an adjuvant containing a C1-5 alkyl ester of a C5-22 alkanoic acid, a C10-20 carboxylic acid, a partial phosphate or partial sulfate of a monohydroxy-functional polyalkyl ether and, as the case requires, an alkylpolyoxyalkylene polyether.    Patent Document 1: WO2007/069771    Patent Document 2: U.S. Pat. No. 6,376,429    Patent Document 3: WO2008/068907    Patent Document 4: WO2001/094339    Patent Document 5: WO2000/53014